1. Field of the Invention
The present invention relates to a current mirror type bandgap reference voltage generator, and in particular to an improved current mirror type bandgap reference voltage generator which is suitable for generating a constant reference voltage regardless of variations in temperature and power voltage, by making use of a current mirror having a large output resistance and a large swing width.
2. Description of the Background Art
In general, a reference voltage generator includes a reference voltage generator using a MOS transistor having a threshold voltage, and a bandgap reference voltage generator using a bipolar transistor. A CMOS bandgap reference voltage generator is discussed in IEEE Journal of Solid-State Circuit, Vol. 34, No. 5, May 1999, entitled by xe2x80x98A CMOS Bandgap Reference Circuit with Sub-1-V Operationxe2x80x99.
In a conventional reference voltage generator, the reference voltage changes due to variations of a power voltage VDD, a temperature and a threshold voltage of a MOS transistor. Accordingly, when the power voltage VDD, the temperature and the threshold voltage of the MOS transistor are varied, the conventional reference voltage generator is not normally operated, thereby causing a mis-operation.
A conventional bandgap reference voltage generator using a differential amplifier will now be explained with reference to FIG. 1.
The conventional bandgap reference voltage generator performs a normal operation only when the voltage of a node Va is greater than xe2x80x98VDSAT.MN23+VTN.MN22+DSAT.MN22xe2x80x99 in an actual DRAM process. But, since the voltage of the node Va is smaller than xe2x80x98VDSAT.MN23+VTN.MN22+DSAT.MN22xe2x80x99, the bandgap reference voltage generator cannot be normally operated. Here, xe2x80x98VDSAT.MN23xe2x80x99 is a drain voltage of an NMOS transistor MN23 in a saturated region, xe2x80x98VTN.MN22xe2x80x99 is a threshold voltage of an NMOS transistor MN22, and VDSAT.MN22 is a drain voltage of an NMOS transistor MN22 in a saturated region.
In addition, the conventional bandgap reference voltage generator using the differential amplifier has a minimum operation voltage VDDmin over 1.4V. Thus, it is not suitable for the DRAM having a low voltage tendency.
Although not illustrated, the conventional reference voltage generator has a disadvantage in that the reference voltage has a variation ratio of 0.44% in a period where the power voltage is 2.5V and the temperature ranges from 20 to 90xc2x0 C., and has a high variation ratio of 0.91% in a period where the power voltage ranges from 2.25V to 2.75V and the temperature is 25xc2x0 C. As a result, the conventional reference voltage generator cannot be relied upon to operate stably.
Accordingly, it is a primary object of the present invention to reduce variations of a reference voltage due to variations of a power voltage, by using a current mirror.
Another object of the present invention is to reduce variations of the reference voltage due to temperature variations, by separately generating a current proportional to an emitter-base voltage and a current proportional to a thermal voltage.
Still another object of the present invention is to reduce a minimum operation voltage of a bandgap reference voltage generator by using a current mirror.
In order to achieve the above-described objects of the invention, there is provided a current mirror type bandgap reference voltage generator. A first current generator generates a first current proportional to a base-emitter voltage. A second current generator generates a second current proportional to a thermal voltage. A reference voltage generator adds the first and second currents, and generates a constant reference voltage regardless of variations in temperature and power voltage. Here, the first current generator includes a first current mirror for receiving the power voltage, generating and outputting the first current to a plurality of output terminals. The second current generator includes a second current mirror for receiving the power voltage, generating and outputting the second current to the plurality of output terminals.